The subject matter disclosed herein relates to motors, and more particularly to a spring loaded gear driven resolver for bearingless high pole count electric machine.
The automotive industry has implemented permanent magnet (PM) electric machines for vehicle propulsion applications. Permanent magnet motors typically have high efficiency and tolerance to large radial air gaps. In automotive applications, the electric machine has been integrated into the vehicle propulsion system, usually mounted in the driveline between the internal combustion engine and the vehicle transmission. Early in the evolution of this vehicle integration, the electric machine rotor was typically supported by its own dedicated set of rotor support bearings. Since rotor support bearings have a low reliability with respect to other components in a PM electric machine, the automotive industry has started to pursue the use of bearingless PM electric machines to increase the reliability of the electric machine, while also decreasing the cost and complexity of the electric machine. Current electric machines include a position sensor (i.e., a resolver) that is mounted on the rotor shaft between the two rotor support bearings, or at one end of the rotor shaft. The resolver can be packaged into the electric machine this way for two primary reasons. First, placing the resolver at the inside diameter of the electric machine utilized previously unused space, thereby reducing the overall size of the electric machine. Second, resolvers need to maintain precise axial and radial alignments, of their rotors to their stators, in order to control the error of the reported rotor position. By installing the resolver rotor on the electric machine rotor, which is supported by a bearing system, both the axial and the radial position of the resolver rotor are held nearly constant relative to the resolver stator. Low cost commercially available resolvers are designed to be mounted to a reasonably small shaft (<2 inches). In current applications, the shaft torque is sufficiently large to require a shaft diameter that is significantly larger than 2 inches. As such, a higher cost and large diameter resolver is implemented. Current resolvers also have drawbacks because accessing the resolver includes removal of the entire electric machine.